JP2010242072A - Rubber composition for coating steel cord - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for coating a steel cord that improves both aging prevention performance and adhesion to the steel cord while not reducing moldability. <P>SOLUTION: Based on 100 pts.wt of diene-based rubber, an organic acid cobalt salt with a cobalt amount of 0.1-0.3 pts.wt and 0.01-5 pts.wt of a tea extract including catechin are blended. The tea extract includes catechin and tea polyphenol other than the catechin. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a rubber composition for coating a steel cord, and more specifically, a rubber for coating a steel cord which is improved in both anti-aging performance and adhesiveness to a steel cord without reducing molding processability. Relates to the composition.

  In recent years, from the viewpoint of consideration for the global environment and effective use of resources, there is a demand for extending the life of pneumatic tires, that is, improving tire durability. For this reason, while improving the durability of the member which comprises a tire, improving the adhesiveness between each member and preventing structural destruction is requested | required.

  In general, when steel cord is used for the belt layer or carcass layer of a pneumatic tire, the rubber composition for coating the steel cord is a compound containing an organic acid cobalt salt to increase the adhesion to the steel cord. (For example, refer to Patent Document 1). This steel cord covering rubber composition can improve durability and prolong its life by increasing anti-aging performance. However, when the blending amount of an anti-aging agent such as an amine-based anti-aging agent is increased in order to increase the anti-aging performance of the rubber composition, there is a problem that the adhesiveness between the rubber composition and the steel cord decreases. For this reason, it has been difficult to improve both the life and adhesion of the coating rubber composition.

  In addition, when an organic acid cobalt salt such as cobalt naphthenate or cobalt neodecanoate is added to the rubber composition, there is a problem in that molding processability deteriorates because the rubber viscosity increases. Since the molding processability affects the stability of the quality of the pneumatic tire and thus greatly affects the durability, a coating rubber composition having a low rubber viscosity and excellent molding processability has been demanded.

JP 2005-53953 A

  An object of the present invention is to provide a rubber composition for coating a steel cord which does not deteriorate the molding processability and improves both the anti-aging performance and the adhesiveness to the steel cord.

  The rubber composition for coating a steel cord of the present invention that achieves the above object is a tea extract containing 0.1 to 0.3 parts by weight of an organic acid cobalt salt as a cobalt amount and 100 parts by weight of a diene rubber and containing catechins. 0.01 to 5 parts by weight, and the tea extract contains catechins and tea polyphenols other than catechins.

  As said tea extract, what contains 1 weight% or more of catechin is preferable. The organic acid cobalt salt preferably contains boron.

  This rubber composition for coating a steel cord is suitable for use in a pneumatic tire.

  The rubber composition for coating a steel cord of the present invention is a tea extraction containing 0.1 to 0.3 parts by weight of an organic acid cobalt salt as a cobalt amount with respect to 100 parts by weight of a diene rubber, and tea polyphenols other than catechin and catechin. Since 0.01 to 5 parts by weight of the product is blended, the tea extract can be used without inhibiting the high level of adhesion between the coating rubber composition obtained based on the organic acid cobalt salt and the steel cord. The anti-aging performance of the composition can be improved. In particular, by including catechin and tea polyphenol other than catechin as a tea extract, the dispersibility of catechin in rubber is better than when catechin alone is blended, and the effect of increasing the antioxidant effect of catechin is obtained. It is done. Moreover, by mix | blending a tea extract, since the viscosity raise of the rubber composition which arises when an organic acid cobalt salt is mix | blended is suppressed, a moldability can be improved.

  In the rubber composition for coating a steel cord of the present invention, the rubber component is a diene rubber, and the diene rubber includes natural rubber, isoprene rubber, butadiene rubber, styrene butadiene rubber, butyl rubber, ethylene propylene diene rubber, and these rubbers. It is made to be at least one selected from terminal-modified rubber. Examples of the terminal-modified functional group include a carbonyl group, an epoxy group, an amine group, a hydroxyl group, an alkoxy group, and a silicate. The diene rubber is preferably natural rubber, isoprene rubber or styrene butadiene rubber. Among these, by using natural rubber, the strength of the rubber composition is increased, so that the adhesiveness with the steel cord can be increased. Such diene rubbers can be used alone or as a plurality of blends.

  The rubber composition for coating a steel cord of the present invention increases adhesion to the steel cord by blending an organic acid cobalt salt. The compounding amount of the organic acid cobalt salt is 0.1 to 0.3 parts by weight, preferably 0.15 to 0.25 parts by weight as the amount of cobalt with respect to 100 parts by weight of the diene rubber. When the blending amount of the organic acid cobalt salt as the cobalt amount is less than 0.1 parts by weight, the initial adhesiveness and aging adhesiveness cannot be sufficiently improved. Moreover, when the compounding amount as a cobalt amount exceeds 0.3 weight part, while the anti-aging performance of a rubber composition will deteriorate, the aging adhesiveness with respect to a steel cord will fall.

  Examples of the organic acid cobalt salts include cobalt naphthenate, cobalt neodecanoate, cobalt stearate, cobalt rosinate, cobalt versatate, cobalt tall oil, cobalt borate neodecanoate, cobalt acetylacetonate and the like. . Among these organic acid cobalt salts, an organic acid cobalt salt containing boron is preferable. For example, a complex salt in which a part of the organic acid is replaced with boric acid or the like is preferable. The organic acid cobalt salt containing boron is preferably cobalt orthoborate having a cobalt content of 20 to 23% by weight. Examples of the organic acid cobalt salt containing boron include Manobond C22.5 and Manobond 680C manufactured by Rhodia, CoMend A and CoMend B manufactured by Jhepherd, and YYNBC-II manufactured by Dainippon Ink & Chemicals, Inc.

  The tea extract containing catechins and tea polyphenols other than catechins blended in the rubber composition for coating steel cords of the present invention functions as an antioxidant, and the anti-aging performance of the rubber composition is blended with an amine-based anti-aging agent. The level can be equal to or higher than that of the case. Moreover, the tea extract containing catechin does not inhibit the action of the above-described organic acid cobalt salt to increase the adhesion between the rubber composition and the steel cord, unlike the amine-based anti-aging agent. For this reason, it is possible to improve the anti-aging performance of the rubber composition for coating a steel cord and to maintain and improve the adhesion between the steel cord and the rubber composition.

  In addition, the tea extract containing catechin suppresses an increase in the rubber viscosity of the rubber composition that occurs when the organic acid cobalt salt is blended, and may further reduce the rubber viscosity. It is possible to maintain and improve the moldability of the product. Generally, a rubber composition containing an organic acid cobalt salt tends to generate gelation because carbon radicals are easily generated during kneading and mixing. For this reason, the viscosity of a rubber composition increases and molding processability deteriorates. In contrast, the rubber composition of the present invention is formulated with a tea extract containing catechin together with an organic acid cobalt salt, so that the tea extract containing catechin instantly generates carbon radicals generated during kneading and mixing. By trapping, the gelation can be suppressed and the increase in the viscosity of the rubber composition can be suppressed. Moreover, in order to improve the dispersibility at the time of kneading | mixing and mixing a rubber composition by mix | blending tea extract containing tea polyphenols other than catechin and catechin, rubber viscosity may be reduced.

  The amount of tea extract containing catechins and tea polyphenols other than catechins is 0.01 to 5 parts by weight, preferably 0.015 to 5 parts by weight, more preferably 0.05 to 5 parts by weight per 100 parts by weight of diene rubber. 3 parts by weight, more preferably 0.1 to 2.5 parts by weight. When the blending amount of the tea extract is less than 0.01 part by weight, the effect of improving the anti-aging performance and lowering the rubber viscosity cannot be obtained. On the other hand, when the blending amount of the tea extract exceeds 5 parts by weight, the anti-aging effect and the rubber viscosity reducing effect become saturated and the cost becomes high, which is not preferable. Moreover, when there is too much compounding quantity, since a mixability deteriorates and the dispersibility of carbon black or a reinforcing filler is deteriorated, it is unpreferable.

  The tea extract used in the present invention contains tea-derived polyphenols. These polyphenols are mainly composed of flavonoids, and examples of flavonoids include flavones, flavonols, flavanols, flavone glycosides, and the like. In addition, condensed tannins are generated by combining a plurality of flavonoids. Of the flavonoids, flavanols are catechins having a flavan-3-ol skeleton.

  In this specification, polyphenols contained in the tea extract are roughly classified into catechins and tea polyphenols other than catechins. The tea extract containing catechins of the present invention contains catechins and tea polyphenols other than catechins. Examples of catechin include epicatechin, epigallocatechin, epicatechin gallate, epigallocatechin gallate, free theaflavin, theaflavin monogallate A, theaflavin digallate and the like. Preferably selected from the group consisting of (+)-catechin, (−)-epicatechin, (+)-gallocatechin, (−)-epigallocatechin, (−)-epicatechin gallate and (−)-epigallocatechin gallate It is good to include at least one kind.

  Further, tea polyphenols other than catechins are tea-derived flavonoids other than catechins and tea polyphenols other than flavonoids. By containing these tea polyphenols, the dispersibility of catechin in rubber is made better than when only catechin is blended. For this reason, while making the antioxidant effect of catechin higher, the synergistic effect with the antioxidant effect of tea polyphenols can be expected.

  In the present invention, the content of catechin in the tea extract is preferably 1% by weight or more, more preferably 2 to 70% by weight, and even more preferably 5 to 50% by weight. If the catechin content is less than 1% by weight, the anti-aging performance and the effect of reducing the rubber viscosity cannot be sufficiently obtained.

  The tea extract used in the present invention is an extract from at least one selected from green tea, oolong tea, and black tea. From these tea leaves or ground tea leaves, water or hot water, an organic solvent is used as an extractant. Extraction may be performed at an extraction temperature of ˜60 ° C. Examples of the organic solvent include methanol, ethanol, isopropanol, ethyl acetate, glycerin and the like. These extractants may be used alone or in combination.

  For the tea extract, the fraction extracted with the above extractant is used. When extracted with water, hot water, or an organic solvent, the extract may be used as it is as a tea extract. However, from the viewpoint of handleability, water is removed from the extract by spray drying or freeze drying. It is recommended to use it in powder form.

  As the tea extract used in the rubber composition for coating a steel cord of the present invention, the above-mentioned tea extract may be used as it is, or an antioxidant comprising a mixture to which other natural compounds and / or surfactants are added. It may be used as an agent. Examples of the natural compound include tocopherol, ascorbic acid, polyphenol excluding tea-derived polyphenol, vegetable oil, animal oil, water and the like. The surfactant is not particularly limited. For example, ethylene glycol, glyceric acid ester, propylene glycol, monoglycerin fatty acid ester, polyglycerin fatty acid ester, sucrose fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid. Preferred examples include esters, propylene glycol fatty acid esters, polyglycerol condensed fatty acid esters, and the like.

  Such an antioxidant is commercially available, for example, Sanphenon DK manufactured by Taiyo Kagaku Co. (tea extract containing 92% by weight of tea-derived polyphenols and 8% by weight of minerals, ash, etc.). 74% by weight and containing tea polyphenols other than catechin), sun flavone HG (tea-derived polyphenols containing 89% by weight, minerals, ash, etc. 11% by weight, and this tea-derived polyphenol is tea catechin 73% %, Including tea polyphenols other than catechins), Sankatol No1 (containing 10% by weight of tea-derived polyphenols and treated with a surfactant, this tea-derived polyphenol is other than tea catechins 70% by weight and catechins (Including tea polyphenols) and the like.

  In the present invention, in order to achieve both the anti-aging performance of the rubber composition and the adhesion to the steel cord at a high level, it is preferable not to add an amine-based anti-aging agent. However, as long as the initial adhesion and aging adhesion between the rubber composition and the steel cord are not impaired, various antioxidants generally used in metal coating rubber compositions such as amine-based antioxidants are blended. May be.

  Various additives commonly used in metal coating rubber compositions such as carbon black, reinforcing agents (reinforcing fillers), vulcanization or crosslinking agents, plasticizers, coupling agents, etc. An additive can be blended, and such an additive can be kneaded by a general method to form a rubber composition, which can be used for vulcanization or crosslinking. As long as the amount of these additives is not contrary to the object of the present invention, a conventional general amount can be used. The rubber composition for coating a steel cord of the present invention can be produced by mixing each of the above components using a known rubber kneading machine such as a Banbury mixer, a kneader, or a roll.

  The rubber composition for coating a steel cord of the present invention can be suitably used as a coating rubber for a steel cord subjected to brass plating. In particular, the rubber composition for coating a steel cord is used for a coated rubber of a brass-plated steel cord for a belt layer of a pneumatic tire, a bead wire insulation, and a steel reinforcing layer. Moreover, since it has the effect of reducing the viscosity of a rubber composition, the moldability of a pneumatic tire is excellent.

  For this reason, the pneumatic tire using the rubber composition for coating a steel cord of the present invention can provide a product with stable quality due to excellent molding processability, anti-aging performance of the coated rubber, and the steel cord and the coated rubber. Therefore, the tire durability is improved, so that the tire life can be prolonged.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, the scope of the present invention is not limited to these Examples.

  10 types of steel cord coating rubber compositions (Examples 1 to 5 and Comparative Examples 1 to 5) having the compositions shown in Tables 1 and 2 were used, and the components excluding sulfur and a vulcanization accelerator were 1.8 L in a sealed type. The mixture was kneaded with a mixer for 3 to 5 minutes, and sulfur and a vulcanization accelerator were added to the released masterbatch and kneaded with an 8-inch open roll to obtain a rubber composition for coating a steel cord. In Tables 1 and 2, the compounding amount as the cobalt amount of each organic acid cobalt salt with respect to 100 parts by weight of the diene rubber is described in the column of “Co content”, and catechin is compounded with respect to 100 parts by weight of the diene rubber. The amount is listed in the “catechin content” column.

  A part of the obtained rubber composition for coating a steel cord was subjected to the Mooney viscosity test shown below. Next, anti-aging performance of a rubber test piece obtained by vulcanizing a rubber composition with a predetermined mold, aging adhesion when a steel cord is coated and vulcanized, and a pneumatic tire as a covering rubber for a belt layer (size 195 / 65R15) The high-speed durability at the time of manufacturing was evaluated by the test methods shown below.

Mooney Viscosity The Mooney viscosity (ML _{1 + 4} ) of the steel cord coating rubber composition was measured using a Mooney viscometer in accordance with JIS K6300 using an L-shaped rotor, preheating time 1 minute, rotor rotation time 4 minutes, temperature 100 The measurement was performed under the conditions of 2 ° C. and ° C. The obtained results are shown in Tables 1 and 2 as an index with Comparative Example 1 as 100. The smaller the “Mooney viscosity” index, the lower the rubber viscosity and the better the moldability.

Aging prevention performance Steel cord coating rubber composition is press vulcanized in a 150mm x 150mm x 2mm mold at 160 ° C for 20 minutes to produce a test piece. No. 3 type dumbbell test in accordance with JIS K6251 A piece was stamped and formed. Each dumbbell test piece was divided into two groups, and one group was heated (aging treatment) at 70 ° C. for 96 hours. Using the dumbbell test pieces before and after the aging treatment, a tensile test was performed under the conditions of a temperature of 20 ° C. and a tensile speed of 500 mm / min, and the tensile stress at 50% elongation was measured. The obtained results were calculated as follows: [(tensile stress after aging treatment-tensile stress before aging treatment) / tensile stress before aging treatment × 100] It was shown in "Anti-aging performance" in Tables 1 and 2 as an index. The smaller this index is, the better the anti-aging performance is.

Aging adhesion An unvulcanized sheet having a thickness of 12.5 mm and a width of 12.5 mm was formed using the obtained rubber composition for coating a steel cord. The steel cord is sandwiched between unvulcanized sheets so that the longitudinal direction of the unvulcanized sheet and the steel cord subjected to brass plating (1 × 6 structure, manufactured by Tokyo Steel Corporation) are orthogonal to each other at 160 ° C., 20 Vulcanization was performed under the condition of minutes, and an adhesion test piece according to ASTM D2229 was produced. Each adhesion test piece was divided into two groups, and one group was heated (aging treatment) at 70 ° C. for 96 hours. The pulling force when pulling out the steel cord from the adhesive test piece before and after the aging treatment was subjected to a pulling test of the steel cord under the condition in accordance with ASTM D2229, and the pulling force (N) was measured. The obtained results are calculated as (retraction force after aging treatment / retraction force before aging treatment × 100) by calculating the retention rate (%) of the extraction force. It was shown in “Aging adhesion” of 2. A larger index means better aging adhesion.

High-speed durability The obtained pneumatic tire was mounted on a rim (15 × 6JJ), filled with oxygen at a pressure of 350 kPa, and aged at 80 ° C. for 5 days. Then, after filling with air with an air pressure of 200 kPa and running on an indoor drum tester conforming to JIS D4230 with a drum diameter of 1707 mm and running at a speed of 80 km / h for 2 hours, the speed was set to 120 km / h. And let it run for 24 hours. Thereafter, every 24 hours, the speed was increased by 10 km / h, and the distance traveled until a tire failure was measured. The obtained results are shown in “High-speed durability” in Tables 1 and 2 as an index with the value of Comparative Example 1 as 100. Higher index means higher speed durability.

The types of raw materials used in Tables 1 and 2 are shown below.
NR: natural rubber, TSR-20
Carbon black: HAF grade carbon black, Seest 300 made by Tokai Carbon
Zinc Hana: Zinc Oxide 3 types manufactured by Shodo Chemical Industry Co., Ltd. Stearic Acid: Beads Stearic Acid YR manufactured by NOF Corporation
Anti-aging agent: Santoflex 6PPD manufactured by Flexis
Tea extract: Taiyo Kagaku Sankator No1, 10% by weight of tea-derived polyphenol, which was treated with a surfactant, the tea-derived polyphenol was tea catechin 70% by weight and tea polyphenols other than catechin Included epicatechin: (-)-epicatechin manufactured by Nacalai Desk Co., 99% by weight of catechin
Organic acid Co-1: Cobalt naphthenate, cobalt content 10% by weight, manufactured by Dainippon Ink and Chemicals Co. Organic acid Co-2: Cobalt stearate, cobalt content 8% by weight, manufactured by Dainippon Ink and Chemicals Co. 3: Cobalt orthoborate, cobalt content 22% by weight, Rhodia Manobond C22.5
Insoluble sulfur: Shikoku Kasei Kogyo Co., Ltd. Mukuron OT-20 (80% sulfur content)
Vulcanization accelerator: Noxeller DZ-G manufactured by Ouchi Shinsei Chemical Co., Ltd.

  As is apparent from Table 2, the rubber compositions of Examples 1 to 5 comprising the rubber composition for coating a steel cord of the present invention have a low Mooney viscosity and excellent molding processability, as well as anti-aging performance and aging adhesiveness. It is excellent. It was also recognized that pneumatic tires using these steel cord coating rubber compositions had improved high-speed durability and improved adhesion to steel cords.

  On the other hand, as is clear from Table 1, the rubber compositions of Comparative Examples 1 to 5 that did not contain a tea extract containing catechin and tea polyphenol other than catechin as in the present invention had Mooney viscosity and anti-aging. Either the performance or the aging adhesiveness is inferior, and the pneumatic tire using these rubber compositions has not been able to obtain the effect of improving the high-speed durability. In particular, the rubber composition prepared in Comparative Example 5 is blended with epicatechin (catechin 99% by weight), but is not blended with tea extract containing both catechin and tea polyphenol other than catechin, The dispersibility of catechin in rubber was poor, and the effect of reducing Mooney viscosity and the effect of increasing the antioxidant effect could not be obtained.

Claims (4)

  100 parts by weight of diene rubber is blended with 0.1 to 0.3 parts by weight of organic acid cobalt salt as a cobalt amount and 0.01 to 5 parts by weight of tea extract containing catechin. A rubber composition for coating a steel cord, comprising catechin and tea polyphenol other than catechin.   The rubber composition for coating a steel cord according to claim 1, wherein the tea extract contains 1% by weight or more of catechin.   The rubber composition for coating a steel cord according to claim 1 or 2, wherein the organic acid cobalt salt contains boron. A pneumatic tire using the steel cord covering rubber composition according to claim 1, 2 or 3.